Producing method of stamper for light guide plate

ABSTRACT

Disclosed is a producing method of a stamper for a light guide plate, wherein the method includes the steps of: cleansing a conductor layer deposited layer; plating the conductor layer with a conductive material; spin coating a photoresist on the plating layer; placing a desired pattern mask, exposing and developing; wet etching the plating layer in a portion where the photoresist is partially removed; removing the remaining photoresist; fabricating a master by nickel plating a completed pattern surface; and releasing the master and nickel plating the master again to produce a stamper.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit under 35 U.S.C. § 119 from Korean PatentApplication No. 2004-102225, filed on Dec. 7, 2004, the entire contentof which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to a producing method of astamper for a light guide plate, more specifically to a producing methodof a wet etched stamper employing a plating process technology.

2. Description of the Related Art

When an LCD (Liquid Crystal Display) device was first developed for usein computer monitors, notebook PCs, and flat TVs, it was rather easy tosee characters with the clear distinction between a light-transmittingregion and a light-intercepting region but this was possible only in thepresence of an external light source with high luminance. Without anyexternal light source present, users had a difficult time to readcharacters in a dark place. An LCD with a BLU (Back Light Unit) was thendeveloped to help the users to be able to see the screen more clearlyeven in the absence of an external light source, as in a cathode raytube. The BLU was installed at the rear side of the LCD, taking visualrecognition into consideration, so that the screen display state can bevisually recognized. A widely-used LCD in recent years includes afluorescent lamp disposed at a side as a light source; a light guideplate for reflecting a light emitted from the fluorescent lamp to an LCDpanel; a case and a reflector sheet disposed at the lower portion of thelight guide plate, in which the reflector sheet reflects otherwise lostlight to minimize a loss of the light; a first diffuser sheet disposedat the upper portion of the light guide plate for diffusing an incidentlight on the LCD panel; a vertical and horizontal prism sheet forcondensing the diffused light; a secondary diffuser sheet disposed onthe upper portion of the prism sheet for diffusing the light emittedfrom the prism sheet at a designated angle; and the LCD panel disposedat the upper portion of the secondary diffuser sheet.

Among other components, the light guide plate plays a key role in theLCD. There are several methods for manufacturing the light guide plate.

First of all there is a printing method. According to this method, alight scattering ink was screen printed on the lower portion of thelight guide plate to vertically scatter an incident light and emit thelight. However the printing method had a low light efficiency (orlight-guide efficiency), and many safety problems were present at hightemperature and high humidity. Also, since the printing process had tobe repeated after the light guide plate was molded, productionefficiency or yield of light guide plates was pretty low.

A number of non-printing methods were then developed to overcome theabove problems. An etching method is a good example of thosenon-printing methods. According to the etching method, a photoresist wasfirst coated and a pattern film was deposited thereon. Later the filmwas exposed, developed and chemically etched. Even though a desiredpattern could be easily obtained by using this method, etching densityand reaction time were difficult to control. As a result,reproducibility was not satisfactory. Also, transparency for forming apattern surface in a desired size was found to be defective.

Many technologies were introduced to enhance the light efficiency (orthe light-guide efficiency) of the light guide plate. Examples of suchattempts include Sandblast, V-Cut, and stamper technologies.

However, the sandblast technology turned out to be very susceptive to achange in injection conditions, and a distribution of brightness on thescreen varied accordingly. In the case of the V-Cut technology, althoughit featured excellent light-guide efficiency and reproducibility, anexcessive amount of time required for the cleansing process and othersoutweighed such merits, proving that the V-Cut technology was notsuitable for the mass production of light guide plates. The typicalstamper technology involves a photoresist to form a micro lens array atan appropriate temperature. Unfortunately however, this technology alsohad weak points in that the size and the thickness of a lens patterncould not be adjusted at the same time. Because the thickness of thelens pattern was determined on the basis of the density of a fabricatedphotoresist and the reflow conditions, it was impossible to make microlens arrays of the same thickness but with different sized patterns. Inaddition, patterning on a prism light guide plate and adjusting size,height and density thereof at the same time were not easy to do, so itseemed very difficult to manufacture a light guide plate the way thelight guide plate was originally designed.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide aproducing method of a stamper for a light guide plate, in which themethod features an easy control on making a change in the size of apattern and the height of a lens, and creation of multi-patterns througha simplified process, thereby maintaining high brightness of a light.

To achieve the above objects and advantages, there is provided aproducing method of a reflective-type stamper for a light guide plate,wherein the method is based on a photographic etching process technologyused in semiconductor industries and a plating process technology usedin the MEMS field.

In an exemplary embodiment of the present invention, the producingmethod of a stamper for a light guide plate includes the steps of:cleansing a conductor layer deposited layer; plating the conductor layerwith a conductive material; spin coating a photoresist on the platinglayer; placing a desired pattern mask, exposing and developing; wetetching the plating layer in a portion where the photoresist ispartially removed; removing the remaining photoresist; fabricating amaster by nickel plating a completed pattern surface; and releasing themaster and nickel plating the released master again to produce astamper.

BRIEF DESCRIPTION OF THE DRAWINGS

The above aspects and features of the present invention will be moreapparent by describing certain embodiments of the present invention withreference to the accompanying drawings, in which:

FIG. 1 is a flow chart describing a producing method of a stamper for alight guide plate according to the present invention; and

FIG. 2 a to FIG. 2 f are cross-sectional views illustrating each step ofthe producing method of a stamper according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the present invention will be described hereinbelow with reference to the accompanying drawings.

FIG. 1 is a flow chart describing a producing method of a stamper for alight guide plate according to the present invention; and FIG. 2 a toFIG. 2 f are cross-sectional views illustrating each step of theproducing method of the stamper.

First of all, a glass 1 having a conductor layer deposited thereon wascleansed (FIG. 2 a). Preferably, the conductor layer is an Indium TinOxide (ITO). Instead of employing the conductor layer deposited glass, aconductive material can be deposited on the glass by using the vacuumdeposition technology.

As shown in FIG. 2 b, a conductive material is plated on the conductorlayer (i.e., the ITO). Examples of the conductive material includemetals such as copper, nickel and chrome. In general, the thickness ofthe metal plating on the conductor layer can be varied, but it ispreferably within several tens of micrometers. A photoresist 4 was thenspin coated on the metal plated layer 3 (FIG. 2 c). A desired patternmask was placed on the top to expose the photoresist 4. The pattern maskwas developed through the exposed photoresist 4 (FIG. 2 d).

The metal plated layer 3 without the photoresist 4 on the top (i.e., aportion where the photoresist is partially removed) is wet etched (FIG.2 e). In other words, the metal plated layer (such as, the copper,nickel or chrome plated layer) is removed by wet etching. A typicallyused etching solution for the wet etching process is a mixture of nitricacid and ultra pure water, or a mixture of sulfuric acid, peroxide andultra pure water. It is important that the etching solution has noinfluence on the photoresist used as a protection purpose and theconductor layer deposited on the surface of the glass. Preferably, themetal plated layer is thoroughly wet etched until the border surfacebetween the conductor layer and the metal plated layer was gone.

In effect, the metal plated layer (such as, the copper, nickel or chromeplated layer) can be formed in such a manner that it has the samethickness with a desired pattern thickness. By wet etching the metalplated layer to a designated depth, one can completely resolve theheight deviation between the resulting height of the metal plated layerand the desired pattern thickness.

Next, the remaining photoresist was removed (FIG. 2 f), and a master wasfabricated by plating the pattern surface with nickel. Then the masterwas released and plated one more time in order to produce a stamper.

In conclusion, by applying the present invention method to themanufacture of a light guide plate featuring an optimized lightdiffusion effect, it becomes easier to fix the pattern size, change ordiversity the pattern size, and adjust the distance between thepatterns. Moreover, the depth of the pattern can be more accurately anduniformly controlled by employing the vacuum deposition and platingtechnologies. These advantages are eventually led to the improvement ofreproducibility, the maintenance of uniform brightness, and theenhancement of the light diffusion effect.

The foregoing embodiment and advantages are merely exemplary and are notto be construed as limiting the present invention. The present teachingcan be readily applied to other types of apparatuses. Also, thedescription of the embodiments of the present invention is intended tobe illustrative, and not to limit the scope of the claims, and manyalternatives, modifications, and variations will be apparent to thoseskilled in the art.

1. A producing method of a stamper for a light guide plate, the methodcomprising the steps of: cleansing a conductor layer deposited layer;plating the conductor layer with a conductive material; spin coating aphotoresist on the plating layer; placing a desired pattern mask,exposing and developing; wet etching the plating layer in a portionwhere the photoresist is partially removed; removing the remainingphotoresist; fabricating a master by nickel plating a completed patternsurface; and releasing the master and nickel plating the released masteragain to produce a stamper.
 2. The method according to claim 1, whereinthe conductive material is selected from copper, nickel and chrome. 3.The method according to claim 1, wherein the etching depth is same withthe thickness of the plating layer.
 4. The method according to claim 1,wherein an etching solution for use in the etching process is a mixtureof nitric acid and ultra pure water, or a mixture of sulfuric acid,peroxide and ultra pure water.